At present, a CD (Compact Disc), a DVD (Digital Versatile Disc), and other optical discs (information recording media) are commercialized and widespread. In recent years, a BD (Blu-ray Disc) has begun to be commercialized as a large-capacity next-generation optical disc. There are various types of BDs, including a BD-ROM (ROM type optical disc), which is a read-only disc; a BD-RE (rewritable or RW type optical disc), which is rewritable; and a BD-R (recordable or R type optical disc), which is a write-once disc. As regards rewritable (BD-RE) and recordable (BD-R) discs, the optimum write power used for a write operation varies from one disc type to another and from one manufacturer to another. Therefore, optical drives (optical read/write apparatuses) need to set optimum write power for each optical disc. However, output write power varies from one drive to another. Therefore, the employed write power setting varies so that satisfactory write operations may not always be performed. Consequently, each drive is configured to perform a test write in a predetermined region of each optical disc and adjust for optimum write power for each optical disc.
As regards the BD-RE and BD-R optical discs, the associated written standard states the use of a write power adjustment method (κ method), which uses predetermined write power Ptarget specific to each medium, predetermined modulation Mind, and parameters κ and ρ. This write power adjustment method, which is based on the κ method, adjusts for the optimum write power in accordance with the relationship between the write power obtained by a test write and the modulation derived from the read signal amplitude of the signal of the write power, and the Ptarget, Mind, κ, and ρ values predetermined for the optical disc.
The BD-RE/BD-R written standard also states the use of a linear fit method, which belongs to the κ method category. The linear fit method first notes the relationship between a plurality of write power levels Pwm set for a test write and the modulation Mm derived from the read signal amplitude of a signal written at each write power level Pwm, then determines an evaluated value Sm=Mm×Pwm within a range close to the predetermined write power Ptarget corresponding to the predetermined modulation Mind for the optical disc and to the predetermined modulation Mind, determines the write power threshold Pth that provides a modulation of zero when the relationship between Pwm and Sm is subjected to linear approximation within the above range, and performs calculations (Popt=κ×ρ×Pth) to determine the optimum write power Popt from the determined Pth value and the parameters κ and ρ for the optical disc.
When the above κ method is used to adjust for the optimum write power, it is possible to minimize the output write power variation among various drives.